Simple sugar concentration sensor and method

ABSTRACT

A glucose sensor comprising an optical energy source having an emitter with an emission pattern; a first polarizer intersecting the emission pattern; a second polarizer spaced a distance from the first polarizer and intersecting the emission pattern, the second polarizer rotated relative to the first polarizer by a first rotational amount Θ; a first optical detector intersecting the emission pattern; a second optical detector positioned proximal to the second polarizer, the first polarizer and the second polarizer being positioned between the optical energy source and the second optical detector, the second optical detector intersecting the emission pattern; a compensating circuit coupled to the second optical detector; and a subtractor circuit coupled to the compensating circuit and the first optical detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/678,452, filed Nov. 8, 2019, pending, which is a continuation of Ser.No. 16/031,026, filed Jul. 10, 2018, now U.S. Pat. No. 10,481,085, whichis a continuation of U.S. patent application Ser. No. 15/582,264, filedon Apr. 28, 2017, now U.S. Pat. No. 10,067,054, which is acontinuation-in-part of and claims the benefit of U.S. patentapplication Ser. No. 15/093,547, filed on Apr. 7, 2016, now U.S. Pat.No. 9,636,052, which is a continuation of and claims the benefit of U.S.patent application Ser. No. 14/822,524 filed Aug. 10, 2015, now U.S.Pat. No. 9,320,463, which is a continuation and claims the benefit ofU.S. patent application Ser. No. 14/293,356 filed Jun. 2, 2014, now U.S.Pat. No. 9,101,308, which is a continuation and claims the benefit ofU.S. patent application Ser. No. 13/950,054 filed Jul. 24, 2013, nowU.S. Pat. No. 8,743,355, which claims the benefit of U.S. ProvisionalPatent Application No. 61/714,731, filed Oct. 16, 2012; all of which areincorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to monitoring of simple sugar (ormonosaccharide) content within a fluid. More specifically, the inventionuses an optical energy source in combination with polarizers todetermine the change in a sugar level (e.g., glucose) of a subject fluidrelative to a baseline concentration, such as blood.

2. Description of the Related Art

Simple sugar changes the polarization of the optical energy passingthrough it according to the equation Θ=α×L×C, where L is the travellength of the energy through the fluid in which the sugar isconcentrated, C is the sugar concentration, and α is a constant thatdepends on the type of sugar, wavelength of the energy, and the fluid.If L and α are known, by measuring the change in polarization of energypassing through a sugar-containing fluid relative to a baselinemeasurement, the sugar concentration of the fluid can be derived.

This principle may be used, for example, to non-invasively determine theglucose concentration of human blood. Normal blood has a non-zeroglucose concentration C, which causes a change in polarization forenergy passing through the blood. For a glucose concentration of 70mg/dL and an α=45.62 (×10⁻⁶) degrees/mm/(mg/dL), energy of wavelength633 nm and a 3.0 mm path length will have a rotation Θ of 0.00958degrees. Measuring the change in rotation caused by the sugar allowsderivation of the current sugar concentration.

SUMMARY OF THE INVENTION

The present invention may be used to monitor sugar (e.g., glucose) in afluid, and provides numerous advantages over traditional techniques thatrely on a standard polarization analyzer, which requires actively movingparts and angular resolution precision to 0.01 degrees. First, thepresent invention is non-invasive, which lowers the risk ofcontamination. Second, the present invention may provide an ability tostream real-time, continuous data. Third, the present invention providesa low operating cost.

The invention includes an optical energy source having an emitter withan emission pattern; a first polarizer intersecting the emissionpattern; a second polarizer spaced a distance from the first polarizerand intersecting the emission pattern, the second polarizer rotatedrelative to the first polarizer by a first rotational amount Θ; a firstoptical detector intersecting the emission pattern; a second opticaldetector positioned proximal to the second polarizer, the firstpolarizer and the second polarizer being positioned between the opticalenergy source and the second optical detector, the second opticaldetector intersecting the emission pattern; a compensating circuitcoupled to the second optical detector; and a subtractor circuit coupledto the compensating circuit and the first optical detector.

In one or more embodiments is described an apparatus for measuringchange in sugar concentration in a fluid relative to a baselineconcentration. The apparatus comprises a source of optical energy, saidsource having an emitter having an emission pattern. The apparatuscomprises a first optical detector spaced a distance from said source.The apparatus comprises a second optical detector collocated with saidfirst optical detector. The apparatus comprises a plurality ofpolarizers optically between said source and said detectors. Theplurality of polarizers comprises a first polarizer intersecting theemission pattern. The plurality of polarizers comprises a secondpolarizer rotated relative to the first polarizer by a first rotationalamount Θ, spaced a distance from the first polarizer, and proximal tosaid second optical detector, wherein said first polarizer is opticallybetween said source and said second polarizer. With the apparatus, thedistance between the first and second polarizers is sufficient to enablethe optical positioning of a volume of liquid intersecting said emissionpattern between said first polarizer and said second polarizer andoptically between the first polarizer and the first detector. Theapparatus comprises at least one circuit coupled to said first opticaldetector and said second optical detector. The at least one circuitcomprises a compensating circuit coupled to said second opticaldetector, a subtractor circuit coupled to said compensating circuit andsaid first optical detector, and a gain circuit coupled to saidsubtractor circuit. With the apparatus, in one or more embodiments, theat least one circuit further comprises a unity gain circuit coupled toand between said first optical detector and said subtractor circuit.With the apparatus, in one or more embodiments, the Θ is 45.028 degrees.With the apparatus, in one or more embodiments, the optical energysource is a near-infrared wavelength optical energy source. With theapparatus, in one or more embodiments, the optical energy source is ared-wavelength energy source. With the apparatus, in one or moreembodiments, the optical energy source is a LED. With the apparatus, inone or more embodiments, the optical energy source is a laser. With theapparatus, in one or more embodiments, the fluid is blood. With theapparatus, in one or more embodiments, the apparatus further comprises aform factor wearable around an ear, said form factor housing the opticalenergy source, the first polarizer, the second polarizer, the firstoptical detector, and the second optical detector. With the apparatus,in one or more embodiments, the Θ is between thirty-five and fifty-fivedegrees (inclusive) of rotation from a baseline rotation caused by abaseline concentration of a simple sugar in a fluid for energy travelinga length L through said fluid. With the apparatus, in one or moreembodiments, the Θ is between forty and fifty degrees (inclusive). Withthe apparatus, in one or more embodiments, the Θ is forty-five degrees.With the apparatus, in one or more embodiments, the plurality ofpolarizers consists of said first polarizer and said second polarizer.With the apparatus, in one or more embodiments, the optical energy isunmodulated. With the apparatus, in one or more embodiments, the opticalenergy consists of one unmodulated light wave.

In one or more embodiments described herein is method of detecting anamount of change of sugar concentration in a subject fluid relative to abaseline concentration. The method comprises directing optical energy ina first direction. The method comprises positioning the subject fluidbetween a first polarizer and a first detector, between said firstpolarizer and a second polarizer rotated relative to the first polarizerby a first rotational amount Θ, and between said first polarizer and asecond detector, wherein said second polarizer is positioned between thefirst polarizer and said second detector. The method comprises passingthe optical energy through the first polarizer to become once-polarizedoptical energy. The method comprises passing the once-polarized opticalenergy through the subject fluid to become rotated once-polarizedoptical energy. The method comprises detecting an intensity of therotated once-polarized optical energy. The method comprises passing atleast a portion of the rotated once-polarized optical energy through thesecond polarizer to become twice-polarized optical energy. The methodcomprises detecting the intensity of the twice-polarized optical energy.The method comprises providing a signal representative of a differencebetween the intensity of the rotated once-polarized optical energy andthe intensity of the twice-polarized optical energy. The methodcomprises correlating the signal to a sugar concentration. With themethod, in one or more embodiments, the optical energy is red-wavelengthoptical energy. With the method, in one or more embodiments, the opticalenergy is near-infrared optical energy. With the method, in one or moreembodiments, the first optical detector is collocated with said secondoptical detector.

In one or more embodiments is a system for measuring a change inpolarization of energy across a fluid. The system comprises a singlesource for emitting energy. The system includes a first polarizer forpolarizing the energy emitted from the source to provide a firstpolarized energy. The system includes a second polarizer for polarizingat least a portion of the first polarized energy and to provide a secondpolarized energy, wherein the second polarizer is rotated by arotational amount with respect to the first polarizer. The systemincludes a first detector for detecting the first polarized energyreceived a distance away from the first polarizer. The system includes asecond detector for detecting the second polarized energy. The systemincludes a module coupled with the first detector and the seconddetector, the module comprising a first unit for receiving output fromthe first detector and a second unit for receiving output from thesecond detector, the module comparing the first and second outputs. Withthe system, in one or more embodiments, the first unit of the modulecomprises an attenuator for reducing at least a portion of the outputfrom the first detector. With the system, in one or more embodiments,the second unit of the module comprises a compensator for boosting atleast a portion of the output from the second detector. With the system,in one or more embodiments, the system comprises a subtractor forreducing at least a portion of the output from the first detector. Withthe system, in one or more embodiments, the energy is in the form oflight emitted in a near infrared frequency range. With the system, inone or more embodiments, the polarizer is selected from a film, wiregrid, holographic wire grid, and beamsplitter. With the system, in oneor more embodiments, the second polarizer is rotated by a rotationalamount that is at least about 45 degrees or a multiple of about 45degrees. With the system, in one or more embodiments, the system furthercomprises a signal amplifier for amplifying output from the module. Withthe system, in one or more embodiments, the system is fitted to an earsuch that the first polarizer is on a first facing surface of an earwhile the second polarizer, the first detector, the second detector andthe module are on an opposing second facing surface of the ear.

In one or more embodiments is a system for measuring a change inpolarization of energy across a portion of a human body part. The systemcomprises a first polarizer for polarizing energy emitted from a sourceand to provide a first polarized energy to a first facing surface of thehuman body part. The system comprises a second polarizer for polarizingat least a portion of the first polarized energy received from the firstpolarizer when positioned on a second opposing facing surface of thehuman body part. The system comprises a first detector for detecting atleast a portion of the first polarized energy when received on thesecond opposing facing surface of the human body part. The systemcomprises a second detector for detecting at least a portion of thesecond polarized energy when received on the second opposing facingsurface of the human body part. The system comprises a module operablycoupled the first detector and the second detector on the secondopposing facing surface of the human body part. The module comprises afirst unit for receiving output from the first detector and a secondunit for receiving output from the second detector. The module utilizesthe outputs from the first and second units to derive a glucoseconcentration. With the system, in one or more embodiments, the secondpolarizer is rotated by a rotational amount with respect to the firstpolarizer. With the system, in one or more embodiments, the rotationalamount is between and includes 35 degrees and 55 degrees. With thesystem, in one or more embodiments, the system further comprises atleast a first band pass filter to filter the output from the firstdetector and a second band pass filter to filter the output from thesecond detector.

Still further is described an apparatus for measuring change in sugarconcentration in a subject fluid. The apparatus comprises a source ofenergy, the source having an emitter with an emission pattern. Theapparatus comprises a first detector spaced a distance from the source.The apparatus comprises a second detector collocated with said firstdetector. The apparatus comprises a plurality of polarizers between thesource and the detectors. The plurality of polarizers comprise at leasta first polarizer intersecting the emission pattern. The plurality ofpolarizers comprise at least a second polarizer rotated relative to thefirst polarizer by a first rotational amount Θ, spaced a distance fromthe first polarizer, and proximal to said second detector, wherein thefirst polarizer is between the source and the second polarizer. With theapparatus, in one or more embodiments, the distance between the firstpolarizer and the second polarizer enables the positioning of a volumeof liquid intersecting the emission pattern between the first polarizerand the second polarizer and optically between the first polarizer andthe first detector. With the apparatus, in one or more embodiments, theapparatus further comprising at least one circuit coupled to the firstdetector and the second detector. With the apparatus, the at least onecircuit comprises a compensating circuit coupled to the second detector,a subtractor circuit coupled to the compensating circuit and said firstdetector, and a gain circuit coupled to said subcontractor circuit. Withthe apparatus, in one or more embodiments, the compensating circuitcomprises a unity gain circuit coupled to and between the seconddetector and the subtractor circuit. With the apparatus, in one or moreembodiments, the compensating circuit comprises an attenuator coupled toand between first detector and the subtractor circuit. With theapparatus, in one or more embodiments, the plurality of polarizersconsists of the first polarizer and the second polarizer. With theapparatus, in one or more embodiments, the energy is unmodulated. Withthe apparatus, in one or more embodiments, the energy source is a LED.With the apparatus, in one or more embodiments, the Θ is betweenthirty-five and fifty-five degrees inclusive of rotation from a baselinerotation caused by a baseline concentration of a simple sugar in a fluidfor energy traveling a length L through said fluid. With the apparatus,in one or more embodiments, the Θ is between forty and fifty degreesinclusive.

An apparatus for measuring change in sugar concentration in a fluidrelative to a baseline concentration is also described herein. Theapparatus comprises a source of energy, said source having an emitterwith an emission pattern. The apparatus comprises a first detectorspaced a distance from said source. The apparatus comprises a seconddetector collocated with said first detector. The apparatus comprises afirst polarizer intersecting the emission pattern. The apparatuscomprises a second polarizer rotated relative to the first polarizer bya first rotational amount Θ, spaced a distance from the first polarizer,and proximal to said second detector, wherein said first polarizer isoptically between said source and said second polarizer. The apparatuscomprises a volume of liquid, said volume intersecting said emissionpattern and positioned between said first polarizer and said secondpolarizer and between said first polarizer and said first detector. Theapparatus comprises at least one circuit coupled to said first detectorand said second detector. The at least one circuit comprises acompensating circuit coupled to said second detector. The at least onecircuit comprises a subtractor circuit coupled to said compensatingcircuit and said first detector. The at least one circuit comprises again circuit coupled to said subtractor circuit.

As mentioned, a noninvasive system for measuring glucose is provided anddiscussed above. The system may further include a feedback circuitconnecting the light source and the first detector and configured toadjust the intensity of the light capable of penetrating body tissue tomaintain the at least some or all of the first polarized light detectedby the first detector within a first portion calibration range.

In various instances, the first portion calibration range is defined byan upper calibration threshold greater than a first target intensityvalue and a lower calibration threshold lesser than a first targetintensity value.

Also as discussed, a method for measuring glucose is provided. Invarious instances, the method also includes providing a feedback circuitconnecting the light source and the first detector and configured toadjust the intensity of the light capable of penetrating body tissue tomaintain the at least some or all of the first polarized light detectedby the first detector within a first portion calibration range.

Yet additionally mentioned, a method for measuring glucose is provided.This method may also provide for adjusting the intensity of the lightemitting from the light source by a feedback circuit connecting thelight source and the first detector, and in response to the firstoutput, wherein the adjusting maintains the first output within a firstportion calibration range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an embodiment of the invention.

FIG. 1B is a system diagram of an embodiment of the invention includingan feedback aspect.

FIG. 2A is a circuit diagram of the circuit described with reference toFIG. 1A.

FIG. 2B is a circuit diagram of the circuit described with reference toFIG. 1B.

FIG. 3A is the system diagram of FIG. 1A showing the embodiment in usewith a human ear.

FIG. 3B is the system diagram of FIG. 1B showing the embodiment in usewith a human ear.

FIG. 4A-4C show actual data from an embodiment of the present inventionused to derive sugar concentrations for three separate cases.

FIG. 5A-5C show the same data shown in FIGS. 4A-4C in a different form,with the unpolarized and polarized waveforms imposed on one another

FIG. 6A-C shows data from an embodiment of the present inventiondemonstrating the effect of the feedback aspect according to FIGS. 1B,2B, and 3B.

DESCRIPTION OF THE VARIOUS EMBODIMENTS

FIGS. 1A-B show an embodiment 20 of the invention, which comprises anoptical energy source 22, a first polarizer 24, a second polarizer 26spaced a distance from the first polarizer 24 having a rotation Θrelative to the first polarizer 24, a first optical energy detector 28,a second optical energy detector 30 collocated with the first detector28, and a circuit 46. Each of the first and second optical detectors 28,30 are oriented to receive optical energy passing through a space 32. Inthe preferred embodiment, the detectors 28, 30 are silicon detectors. Asused herein, “collocated” means being positioned adjacent each other sothat, all else being equal, light from a common source will enter eachof the detectors with approximately equal intensity. In addition,although the embodiment discloses the use of silicon detectors, othertypes of detectors may be used (e.g., photoresistors). As shown in FIG.1B, in various instances, a feedback circuit 101 interconnects theoptical energy source 22 and the first optical energy detector 28,although in yet further instances, the feedback circuit 101 mayinterconnect the optical energy source 22 and the second optical energydetector 30. The feedback circuit 101 operates to adjust the sourceoptical energy magnitude of the optical energy from the optical energysource 22 in response to the energy of the optical energy received atthe first optical energy detector 28, or in yet further instances, thesecond optical energy detector 30.

When actuated, the energy source 22 produces initial optical energy 34having an emission pattern 36. The energy source 22 is preferably a redlight source, such as a red light-emitting diode (LED) or a laser, butmay alternatively be near-infrared. Ultimately, the initial opticalenergy 34 must be of a wavelength that may be affected by the presenceof sugar in the subject fluid while also passing through the othervessel in which the fluid is contained. The initial optical energy 34from the optical energy source 22 has a magnitude termed the sourceoptical energy magnitude.

The first polarizer 24 is positioned proximal to the source 22, suchthat the initial optical energy 34 passes through the first polarizer 24and becomes polarized energy 38. The polarized energy 38 traverses thespace 32 between the first and second polarizer 24, 26, where a firstportion 40 of the polarized energy 38 is detected by a first opticaldetector 28 and a second portion 42 of the polarized energy 38 passesthrough a second polarizer 26 to the second optical energy detector 30.Notably, first detector and second detector 28, 30 are collocated,despite the proximity of second polarizer 26 to the second detector 30.Because the space 32 is empty in FIG. 1, the polarized energy 38 passingthrough the space 32 is not rotated by, for example, the presence of asugar in a fluid.

Preferably, the first and second polarizers 24, 26 are alinearly-polarized film because such film is inexpensive compared toother available alternatives. Such film, however, is optimal for energywavelengths in the visible spectrum. Other polarizers may be used,provided that the selected wavelength of the energy source 22 is chosento optimally correspond. For example, an alternative polarizer may bewire-grid or holographic, which is optimally configured for use in thepresent invention with energy of near-infrared and infrared wavelengths.

In various embodiments, the first and second polarizers 24, 26 eachcomprise a keying notch. A keying notch may comprise a cutout of thepolarizer that corresponds to a tab in a housing. In variousembodiments, the keying notch and/or tab may be positioned to establisha difference in rotation between the polarizers 24, 26. Moreover, invarious instances, the first and second polarizers 24, 26 are alinearly-polarized film prepared by CNC cutting. Consequently, invarious embodiments, the linearly-polarized film may have a keying notchprepared by CNC cutting.

Preferably, the difference in rotation between the polarizers 24, 26 isforty-five degrees (or an integral multiple of forty-five degrees) plusthe rotation caused by the baseline. In this optimal case, a change inconcentration relative to the baseline at least initially moves alongthe most linear portion of a sine wave, which makes detecting the changein rotation easier compared to moving further away from where the slopeof the wave is 1 and further towards where the slope is 0 (i.e., thecrest and troughs of the sine wave). For example, when used with abaseline glucose concentration 100 mg/dL over a length of L, Θ equals0.014 degrees. In this case, the rotation between the polarizers shouldbe 45.014 degrees. The greater the change in concentration from thebaseline, however, the more non-linear the correlation of the rotationto the change in concentration.

The first and second detectors 28, 30 are electrically coupled to thecircuit 46. The circuit 46 has a compensating circuit 48, a subtractorcircuit 50, and a gain circuit 52. The first detector 28 is directlycoupled to the subtractor circuit 50. The second detector 30 is coupledto the compensating circuit 48, which boosts the gain of the signalproduced by the second detector 30 by an amount sufficient to compensatefor the loss of intensity attributable to the portion 42 of polarizedenergy 38 passing through the polarized film and the effects ofpolarization due to the baseline concentrations in the fluid, but thecompensating circuit 48 does not compensate for the loss in intensityresulting from changes in polarization due to the concentration changefrom some baseline itself. The subtractor circuit 50 produces a signalthat is the difference between the signals received from the first andsecond detectors 28, 30. The gain circuit 52 amplifies the signal to ausable level.

Notably, in alternative embodiments, the compensating circuit 48 may bean attenuator coupled to the first detector 28 to equalize the intensityof the received optical energy, with the objective being that thedifference in energy seen by the first detector 28 and the seconddetector 30 relates to the rotation of the energy rather than itsamplitude. Similarly, the subtractor circuit 50 may be replaced by aWheatstone or similar bridge.

In further embodiments, the circuit 46 is configured to integratenumerical model improvements to increase stability and consistentresponse to glucose via a feedback aspect, such as an open loop feedbackmethod. Thus, as shown in FIG. 1B, a feedback circuit 101 may beincluded as an aspect of circuit 46 and as explained above. For example,in various instances the circuit 46 would primarily involve coupling theamount of transmitted light detected at the reference detector, such asa first detector 28, and adjusting the LED drive current provided to theoptical energy source 22 to maintain a constant detected amplitude atthe first detector 28. The ability to control optical energy source 22,and more specifically, the LED associated with the optical energy sourcewill fall in a range of capability of the LED driver circuit. A furtheraspect also implemented in this embodiment involves aspects to addressan observed ‘roll-off’ identified at high range glucose values. Theartifacts may be predicted to be based in a combination of specificcomponent parts choices such as may develop through tolerance stack upor nominal value drift. As such, the circuit 46 may include offsetcorrection that allow for correction for both photodiodes and amplifiedcomponents. By maintaining a constant detected amplitude at the firstdetector 28, a change in concentration relative to the baseline may bemore accurately and precisely detected as the change at least initiallymoves along the most linear portion of the sine wave, because themaintaining of a constant detected amplitude compensates for common modepath attenuation and/or differential mode path attenuation, arising frominconsistencies in the placement of the optical energy source 34 and/orfirst detector 28 and/or second detector 30 relative to a tissue undertest, such as a human ear tissue (see FIG. 3B).

Attenuation of the light may flatten the slope of the line comparing thedifferential intensity/polarization of the light at the first detector28 and/or second detector 30 to the amount of glucose in the blood ofthe tissue under test. By implementing a feedback circuit 101 tomaintain the intensity of the light at or near a target value at one ofthe detectors (such as first detector 28), the relationship of glucosein the blood to differential intensity/polarization of the light at thefirst detector 28 and/or second detector 30 may more accurately bemeasured by maintaining the intensity within a known region of theresponse curve. Moreover, the circuit 46 may implement a computationalmodel wherein the bulk tissue scattering of the light passing throughthe tissue may be considered to include three components: (1) bulkattenuation (optical power loss) which is compensated by the feedback,(2) unpolarized transmitted light (scattered light), and (3) polarizedlight (ballistic photon fraction).

Referring to FIG. 2A, the outputs of the first and second detectors 28,30 are provided to the circuit 46. The circuit 46 comprises thecompensating circuit 48 having a potentiometer Ro1, the subtractorcircuit 50, first and second 30-Hz low pass filters that included Ro1and C1, and Ro2 and C2, and the gain circuit 52. The subtractor circuit50 and the gain circuit 52 incorporate an OPA 211KP operationalamplifier IC 66. The low pass filters reject any noise at the detectors28, 30. Polarized output 53 and the unpolarized outputs 55 are fed tothe subtractor circuit 50, which comprises Ro3, Ro4, R13 and R14. Thesubtractor circuit output 54 is then provided to the gain circuit 52comprising Ro5 and C3. The final signal is provided at the gain circuitoutput 56. The embodiment includes an optional unity gain circuit 57 forphase-matching purposes. In various embodiments, all or a portion ofcircuit 46 and/or compensating circuit 48 comprises anapplication-specific integrated circuit (ASIC). For instance, multiplecomponents may be packaged as a single integrated circuit, enablingfurther miniaturization of the circuit 46.

Referring to FIG. 2B further example embodiments of circuit 40 includingthe feedback circuit 101 are depicted. Referring to FIG. 2A and FIG. 2B,the operation of the feedback circuit 101 of FIG. 2B would be akin to(with reference to FIG. 2A) maintaining a constant optical detectedpower on first detector 28 (e.g., the detector receiving light passingthrough polarizer 24 rather than the detector receiving light passingthrough both polarizers 24 and 30). Changes in power to first detector28 would result in a signal altering the supplied optical energyincident on the total detection system from an optical source 22 (LED,laser, and/or similar source), not shown in FIG. 2A.

FIGS. 3A-B show the embodiment 20 in use with a human ear 68, at least aportion of which occupies the space 32. The preferred orientation of theear 68 within the space 32 is so that the polarized energy 38 passesthrough the ear 68 generally parallel to a lateral axis, where L is thedistance along the axis of the measured fluid. For most human ears, L isapproximately three millimeters of capillary-rich and blood vessel-richskin.

When actuated, the energy source 22 produces initial optical energy 34having the emission pattern 36. The initial energy 34 passes through thefirst polarizer 24, and is of a wavelength to which the non-sugarcomponents of the ear 68 (i.e., skin, blood, tissue, cartilage) are, toat least some extent, transparent.

After passing through the first polarizer 24, the initial energy 34becomes polarized energy 38. Glucose within the blood in the ear 68,however, will cause a change in polarization of the energy 38 accordingto Θ=α×L×C, causing the rotated energy 70 exiting the ear to have afirst rotation Θ₁.

The intensity of a first portion 72 of the rotated energy 70 is detectedby the first detector 28. The intensity of a second portion 74 of therotated energy 70 passes through the second polarizer 26 and is detectedby the second detector 30. Each of the first and second detectors 28, 30produces a signal representative of the received intensity. Because theintensity of the rotated energy 70 received by the second detector 30 isonly the intensity of the rotated energy component passing through thesecond polarizer 26, by measuring the difference in intensities at thedetectors 28, 30, the rotation caused by the glucose in the ear 70 canbe derived, from which the changed in glucose concentration relative toa baseline can be determined.

To determine the baseline, prior to use, the embodiment 20 is calibratedto a baseline glucose concentration of seventy mg/dL (a “normal”concentration for human blood) by changing a potentiometer, such aspotentiometer 60 (FIG. 2A) to compensate for the difference inintensities of energy received by the first and second detectors 28, 30.Thus, any change in measured rotation represents a change in glucoseconcentration from some baseline (e.g., 70 mg/dL).

An alternative embodiment of the invention is calibrated to a baselineglucose concentration of 100 mg/dL using wavelength of 650 nm, resultingin a rotation of 45.028 degrees of the second polarizer relative to thefirst polarizer. This results range of resulting rotation of thebaseline plus or minus 0.2 degrees for a glucose concentration ofbetween 30 mg/dL and 300 mg/dL. Thus, a glucose concentration of 30mg/dL will result in a rotational difference between the detectors of0.0096 degrees, whereas a glucose concentration of 300 mg/dL will resultin a rotational difference of 0.0273 degrees in the opposite directionof the direction of the 30 mg/dL concentration.

With specific reference to FIG. 3B in combination with FIG. 2B, notably,and differently from the discussion with reference to FIG. 2A and FIG.3A above, a feedback circuit 101 conveys a feedback signal from firstdetector 28 to the energy source 22 producing initial optical energy 34.The feedback circuit 101 adjusts the energy source 22 to maintain thefirst portion 72 of the rotated energy within a first portioncalibration range. More specifically, in response to the energy of theintensity of the first portion 72 of the rotated energy 70 deviatingbelow a lower calibration threshold from a first target intensity value,the feedback signal directs the energy source 22 to increase theintensity of the initial optical energy 34 (source optical energymagnitude) until the intensity of the first portion 72 of the rotatedenergy 70 no longer falls below a lower calibration threshold from afirst target intensity value. Similarly, in response to the intensity ofthe first portion 72 of the rotated energy 70 deviating above an uppercalibration threshold from a first target intensity value, the feedbacksignal directs the energy source 22 to decrease the intensity of theinitial optical energy 34 (source optical energy magnitude) until theintensity of the first portion 72 of the rotated energy 70 no longer isabove the upper calibration threshold from the first target intensityvalue. The upper calibration threshold and the lower calibrationthreshold define the boundaries of the first portion calibration range.

While the difference between the intensity of the first portion 72 andthe second portion 74 of the rotated energy is measured similarly to asdiscussed above, the intensity of the first portion 72 is maintainedbetween the upper calibration threshold and the lower calibrationthreshold about the first target intensity value. Because the opticaltransmissivity of the ear 70 changes exponentially with the tissuethickness, and yet the difference in intensity of the first portion 72and second portion 74 relates to the glucose concentration according toa linear approximation, relatively small changes in tissue thickness canresult in relatively large shifts along a numerical approximation curve,causing calculation errors. Consequently the feedback mechanismdiscussed herein maintains the comparison within the same or similarlinear region of the approximation curve, aiding calculation accuracy.

As previously mentioned, to determine the baseline, prior to use, theembodiment 20 is calibrated to a baseline glucose concentration ofseventy mg/dL (a “normal” concentration for human blood) by changing apotentiometer, such as potentiometer 60 (FIG. 2A) to compensate for thedifference in intensities of energy received by the first and seconddetectors 28, 30. Thus, any change in measured rotation represents achange in glucose concentration from some baseline (e.g., 70 mg/dL).

An alternative embodiment of the invention is calibrated to a baselineglucose concentration of 100 mg/dL using wavelength of 650 nm, resultingin a rotation of 45.028 degrees of the second polarizer relative to thefirst polarizer. This results range of resulting rotation of thebaseline plus or minus 0.2 degrees for a glucose concentration ofbetween 30 mg/dL and 300 mg/dL. Thus, a glucose concentration of 30mg/dL will result in a rotational difference between the detectors of0.0096 degrees, whereas a glucose concentration of 300 mg/dL will resultin a rotational difference of 0.0273 degrees in the opposite directionof the direction of the 30 mg/dL concentration.

Notably, in various instances the feedback circuit 101 operates so thatthe determined baseline may be further adjusted to compensate forvariations in the intensity of the first portion 72 of the rotatedenergy 70 detected by the first detector 28 and/or the intensity of thesecond portion 74 of the rotated energy 70 passed through the secondpolarizer 26 and detected by the second detector 30. For instance,variations in placement of the human ear 68 at least a portion of whichoccupies the space 32 may cause variations in the intensity of the firstportion 72 and/or the intensity of the second portion 74. As such, invarious instances, a feedback circuit 101 of the circuit 46 may causethe intensity of the first portion 72 or the intensity of the secondportion 74 to be returned to at or near the determined baselineregardless of the relative inconsistency of positioning on the human ear68. As a result, the rotation caused by the glucose in the ear 70 can bederived. As mentioned, because the intensity of the rotated energy 70received by the second detector 30 is only the intensity of the rotatedenergy component passing through the second polarizer 26, by measuringthe difference in intensities at the detectors 28, 30, the rotationcaused by the glucose in the ear 70 can be derived, from which thechanged in glucose concentration relative to a baseline can bedetermined.

Rather than changing the potentiometer 60 to compensate for thedifference in intensities of energy received by the first and seconddetectors 28, 30 to calibrate the embodiment 20 to a baseline glucoseconcentration of seventy mg/dL (a “normal” concentration for humanblood), instead, the device may actively implement feedback via thefeedback circuit 101 to continuously or intermittently recalibrate sothat any change in measured rotation represents a change in glucoseconcentration from some baseline (e.g., 70 mg/dL). By controllingfeedback circuit 101, the circuit 46 may learn compensation offsetvalues and may store these values in a memory rather than requiring thechanging of the potentiometer 60. In this manner the feedback circuit101 may operate to account for circuit variations and allowrecalibration of the relationship between measured rotation and changein glucose concentration from a base line. In this manner, the feedbackcircuit 101 may operate so that the slope intercept calculations mayremain unhampered by the exponential effect on photon transmissivity ofthe ear 70 (and associated exponential effect on intensity of detectedlight) that is caused by a linear change in a thickness of ear 70. Thusthe feedback circuit 101 may be multipurpose.

In various instances, there are at least two methods for calibrating theinvention. First and preferably, during fabrication of each sensor, asample control serum or a similar component that would rotate thepolarization state a known amount would be inserted in the space. Thiscontrol would provide a simulated known glucose concentration for use inadjusting the device to the proper calibrated settings. Alternatively,the user/wearer can take an initial reading with the sensor andadditionally take a near-simultaneous reading with another glucosesensor (e.g., a blood stick meter). This value from the other sensorwould be input into the sensor with user input means such as knobs,buttons and the like connected to a microcontroller.

FIGS. 4A-4C shows actual data from an embodiment of the invention usedto detect glucose concentrations of 75 mg/dL, 150 mg/dL, and 300 mg/DL.The left side of each example shows actual signals received from thepolarized detector 28 and the non-polarized detector 30. The right sideof each example shows the output of the subtractor circuit. Theembodiment is calibrated for a baseline of 75 mg/dL. In FIG. 4A, thesubtractor circuit averages to zero, indicating no change from thebaseline. In FIG. 4B, the subtractor circuit averages to approximately0.00005 Volts. In FIG. 4C, the output of the subtractor circuit averagesto approximately 0.0001 Volts, or twice the middle example, which isexpected give that the concentration of the bottom example is twice theconcentration of shown in FIG. 4B.

FIGS. 5A-5C show the same data depicted in FIGS. 4A-4C, but with theunpolarized and polarized waveforms on the same graph. FIG. 5Acorresponds to the data shown in FIG. 4A. FIG. 5B corresponds to thedata shown in FIG. 4B. FIG. 5C corresponds to the data shown in FIG. 4C.

FIGS. 6A-C illustrate the operative effects of the feedback circuit 101.FIG. 6A depicts the linear relationship of the intensity of lightreceived by a detector as represented by the mA of current conductedthrough a detector versus the mg/dL concentration of glucose. FIG. 6Billustrates the divergence of this linear relationship arising fromuncompensated attenuation of the optical energy, whereas FIG. 6C showsthe calibrating effect on this linear relationship arising fromcompensating for attenuation of the optical energy by a feedback circuit101.

The present disclosure includes preferred or illustrative embodiments inwhich specific sensors and methods are described. Alternativeembodiments of such sensors can be used in carrying out the invention asclaimed and such alternative embodiments are limited only by the claimsthemselves. Other aspects and advantages of the present invention may beobtained from a study of this disclosure and the drawings, along withthe appended claims.

1. A noninvasive system for passing optical energy through afluid-containing tissue to measure a glucose concentration therein, thesystem comprising: a light source providing a first light; a polarizerreceiving the first light and providing a second light, the first lightand the second light being at least partially differently polarized; afirst detector positioned to detect at least some or all of the firstlight; and a second detector positioned to detect at least some or allof the second light; a circuit, in which a first output from the firstdetector, and a second output from the second detector are each providedto the circuit, the circuit for producing at least a third output as adifference between the first output and the second output, wherein (i)the light source and (ii) the first and second detectors are configuredto receive the fluid-containing tissue between (i) the light source and(ii) the first and second detectors, and wherein the difference betweenthe first output and the second output corresponds to a magnitude of theglucose concentration in the fluid-containing tissue.
 2. The noninvasivesystem of claim 1, the system further comprising a feedback circuitconnecting the light source and the first detector and adjusting anamplitude of the light source to maintain an intensity of a portion ofthe first light detected by the first detector within a first portioncalibration range.
 3. The noninvasive system of claim 2, wherein thefirst portion calibration range is defined by an upper calibrationthreshold greater than a first target intensity value and a lowercalibration threshold lesser than the first target intensity value. 4.The noninvasive system of claim 1, further comprising a furtherpolarizer between the light source and the polarizer and polarizing thefirst light, wherein the polarizer and the further polarizer aredifferentially rotated.
 5. The noninvasive system of claim 1, furthercomprising a further polarizer between the light source and thepolarizer and polarizing the first light, wherein the polarizer and thefurther polarizer are differentially rotated, the differential rotationcomprising about forty five degrees, or a multiple thereof.
 6. Thenoninvasive system of claim 1, wherein the circuit comprises aWheatstone bridge configured to produce the third output as thedifference between the first output and the second output.
 7. Thenoninvasive system of claim 1, further comprising a circuit at least oneof increasing and decreasing the first output of the first detector andthe second output of the second detector.
 8. A method for passingoptical energy through a fluid-containing tissue to measure a glucoseconcentration therein, the method comprising: positioning a polarizer tobe illuminated by a light source, wherein a combination of the lightsource and the polarizer provides a first light and a second light,wherein the second light is polarized by the polarizer; positioning afirst detector to detect at least some or all of the first light, thefirst detector providing a first output; positioning a second detectorto detect at least some or all of the second light, the second detectorproviding a second output, wherein (i) the light source and (ii) thefirst and second detectors are configured to receive thefluid-containing tissue between (i) the light source and (ii) the firstand second detectors; and comparing a magnitude of the first output andthe second output to determine a difference, wherein the differencebetween the first output and the second output corresponds to amagnitude of the glucose concentration in the fluid-containing tissue.9. The method of claim 8, further comprising providing a feedbackcircuit connecting the light source and the first detector.
 10. Themethod of claim 9, further comprising adjusting an amplitude of thelight source in response to a feedback from the feedback circuit tomaintain an amplitude of the first output within a first portioncalibration range.
 11. The method of claim 10, wherein the first portioncalibration range is defined by an upper calibration threshold greaterthan a first target intensity value and a lower calibration thresholdlesser than the first target intensity value.
 12. The method of claim 9,further comprising providing a further polarizer between the lightsource and the polarizer and polarizing the first light, wherein thepolarizer and the further polarizer are differentially rotated.
 13. Themethod of claim 9, further comprising providing a further polarizerbetween the light source and the polarizer and polarizing the firstlight, wherein the polarizer and the further polarizer aredifferentially rotated, the differential rotation comprising about fortyfive degrees, or a multiple thereof.
 14. The method of claim 9, whereinthe comparing the magnitude of the first output and the second output todetermine the difference comprises producing a third output from aWheatstone bridge as the difference between the first output and thesecond output, wherein a magnitude of the third output corresponds tothe magnitude of the glucose concentration in the fluid-containingtissue.
 15. The method of claim 9, wherein the comparing the magnitudecomprises providing a circuit for receiving the first output and thesecond output, the circuit comprising at least a subtractor forproducing at least a third output as the difference between the firstoutput and the second output.
 16. A noninvasive system for passing anoptical energy through a fluid-containing tissue, the system comprising:a polarizer for receiving a first light from a light source, wherebythere is created, from the first light, a second light polarizeddifferently than the first light; a first detector positioned to detectthe first light; and a second detector positioned to detect the secondlight, wherein (i) a light source and (ii) the first and seconddetectors are configured to receive the fluid-containing tissue between(i) the light source and (ii) the first and second detectors.
 17. Thenoninvasive system of claim 16, further comprising a feedback circuitinterconnecting the light source to the first detector and configured toadjust an intensity of the first light to maintain the detected firstlight detected by the first detector within a first portion calibrationrange.
 18. The noninvasive system of claim 16, wherein a differencebetween a first output of the first detector and a second output of thesecond detector corresponds to a difference in magnitude of the firstlight and the second light.
 19. The noninvasive system of claim 18,wherein the difference in magnitude of the first light and the secondlight corresponds to a glucose concentration in the fluid-containingtissue.
 20. The noninvasive system of claim 16, further comprising afurther polarizer between the light source and the polarizer andpolarizing the first light, wherein the polarizer and the furtherpolarizer are differentially rotated.